Article: Biology » Coat
The coat of the domestic dog (Canis lupus familiaris) refers to the hair that covers its body. A dog’s coat may be a double coat, made up of a soft undercoat and a coarser topcoat, or a single coat, which lacks an undercoat. The terms fur and hair are often used interchangeably when describing a dog’s coat, however in general, a double coat, e.g., like that of the Newfoundland and most mountain dogs, is referred to as a fur coat, while a single coat, like that of the Poodle, is referred to as a hair coat.
Colors, patterns, lengths & textures
There is a greater variety of coat colors, patterns, lengths and textures found in the domestic dog than in its wolf relations, even though dogs and wolves belong to the same species (Canis lupus). Coat colors in dogs were not likely initially selected for by humans but were probably the inadvertent outcome of some other selection process (i.e. selection for tameness). Research has found that tameness brings associated physical changes, including coat coloring and patterning.
Domestic dogs often display the remnants of counter shading, a common natural camouflage pattern. The basic principle of counter shading is when the animal is lit from above, shadows will be cast on the ventral side of the body. These shadows could provide a predator or prey with visual cues relating to the movement of the animal. By being lighter colored on the ventral side of the body, an animal can counteract this, and thereby fool the predator or prey. An alternative explanation is that the dorsal and ventral sides of an animal experience different selection pressures (from the need to blend in to different backgrounds when viewed from above and below) resulting in differing coloration.
Genetic basis of color & pattern
Modern breeds of dog exhibit a diverse range of coat colorings, patterns, lengths and textures. In recent years, the understanding of the genetic basis for coat coloring and patterning and coat length and texturing has increased significantly.
There are currently eight known genes within the canine genome that are associated with coat color. Each of these genes occurs in at least two variants, or alleles, which accounts for the variation in coat color between animals. Each of these genes exists at a fixed location, or locus, of the animal’s genome.
The coat of most dogs grows to a specific length and then stops growing, while the coats of some dogs grow continuously in a manner similar to human hair growth. Examples of breeds of dog whose coats grow continuously are:
Irish Water Spaniel
Kerry Blue Terrier
Portuguese Water Dog
Soft Coated Wheaten Terrier
Corded coats, like those of the Puli and Komondor are thought to be the result of continuously growing curly coats. Other breeds with continuously growing curly coats, such as the Poodle, can also be groomed to cord.
Some breeds of dog do not grow hair on parts of their bodies and may be referred to as “hairless. Examples of “hairless” dogs are the Xoloitzcuintli (Mexican Hairless Dog), the Peruvian Inca Orchid (Peruvian Hairless Dog) and the Chinese Crested. Research suggests that hairlessness is caused by one or more dominant alleles, one or more of which is homozygous lethal.
Hairless and Coated Xoloitzcuintli.
Genetic testing & phenotype prediction
In recent years genetic testing for the alleles of some genes has become available Software is also available to assist breeders in determining the likely outcome of matings.
The nature and quality of a purebred dog’s coat is important to the dog fancy in the judging of the dog at conformation shows. The exact requirements are detailed in each breed’s breed standard and do not generalize in any way, and the terminology may be very different even when referring to similar features. See individual breed articles for specific information.
Every hair in the dog coat grows from a hair follicle, which has a cycle of growing, then dying and being replaced by another follicle. When the follicle dies, the hair is shed (moults). The length of time of the growing and shedding cycle varies by breed, age, and by whether the dog is an inside or outside dog.
Many dogs shed their undercoat each spring and regrow it again as colder weather comes in; this is also referred to as blowing the coat. Many domesticated breeds shed their coat twice a year. In some climates, the topcoat and undercoat might shed continuously in greater and smaller quantities all year.
Some dog breeds have been promoted as hypoallergenic (which means less allergic, not free of allergens) because they shed very little. However, no canine is known to be completely non-allergenic. Often the problem is with the dog’s saliva or dander, not the fur. Although poodles and terriers (and mixes of poodles and terriers) are commonly represented as being hypoallergenic, the reaction that an individual person has to an individual dog may vary greatly. In treating dog related allergies, it has been found that “Factors related to individual dogs seem to influence the allergenicity more than breed…”
References & Notes:
- James Serpell, ed (1995). The Domestic Dog: It’s Evolution, Behaviuor and Interactions with People. Cambridge, United Kingdom: Cambridge University Press. p. 284. ISBN 0521425379.
- Lyudmila N. Trut (March–April 1999). “Early Canid Domestication: The Farm-Fox Experiment”. American Scientist 87 (2): 160–169. doi:10.1511/1999.2.160.
- Graeme D. Ruxton, Michael P. Speed & David J. Kelly (September 2004). “What, if anything, is the adaptive function of countershading?”. Animal Behaviour 68 (3): 445–451. doi:10.1016/j.anbehav.2003.12.009.
- Schmutz, S. M. & Berryere, T. G. (December 2007). “Genes affecting coat colour and pattern in domestic dogs: a review”. Animal Genetics 38 (6): 539–549. doi:10.1111/j.1365-2052.2007.01664.x. PMID 18052939.
- Edouard Cadieu, Mark W. Neff, Pascale Quignon, Kari Walsh, Kevin Chase, Heidi G. Parker, Bridgett M. VonHoldt, Alison Rhue, Adam Boyko, Alexandra Byers, Aaron Wong, Dana S. Mosher, Abdel G. Elkahloun, Tyrone C. Spady, Catherine André, K. Gordon Lark, Michelle Cargill, Carlos D. Bustamante, Robert K. Wayne, Elaine A. Ostrander (October 2009). “Coat Variation in the Domestic Dog Is Governed by Variants in Three Genes”. Science 326 (5949): 150–153. doi:10.1126/science.1177808. PMC 2897713. PMID 19713490.
- Sheila M. Schmutz (December 27, 2008). “Coat Color Alleles in Dogs”.
- “Breeders Assistant”. Premier Pedigree Software. 2009.
- Grady, Denise (February 5, 1997). “Nonallergenic Dog? Not Really”. New York Times.
- Heutelbeck ARR, Schulz T, Bergmann K, Hallier E (Jan 2008). “Environmental Exposure to Allergens of Different Dog Breeds and Relevance in Allergological Diagnostics”. Journal of Toxicology and Environmental Health, Part A 71 (11-12): 751–8. doi:10.1080/15287390801985513. PMID 18569573.
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